#include<stdio.h>

/*全局变量声明*/
int a = 20;

int main()
{
    /*在函数中的局部变量声明*/
    int a = 10;
    int b = 20;
    int c = 0;
    int sum(int, int);

    printf("value of a in main() = %d\n", a);
    c = sum(a, b);
    printf("value of c in");
}
